I think this is one of the most annoying arguments in football 'you just don't understand what he does'. I do, but I don't think he's as good at it as some people think.
If he's there to do Barry's running, why does barry often cover more ground? If he's there to cover the fullback, why do we get exposed down the flanks so often?
I Don't think he's useless, but I think he's massively overrated by many fans.
I think you are absolutely right. People should be able to explain what players do if it's so clear to say what people are missing. I agree with your analysis too, but what I'd ask though is how far is that McCarthy and how far is it a tactical switch we have made?
McCarthy seems to me (before Sunday) a bit caught between positions. I don't think it's been clearly defined what his role is. I think he was expected to not be as defensive as Barry but also not go forward to much. He was getting a bit caught for me between two positions, of defensive midfield or a box to box midfielders and really doing neither. In principle he is meant to cover our fullbacks, but with Coleman being injured and Browning less offensive that has left him again a bit wasted.
I am glad the hand breaks are off now. Until we move Barry on (which I don't think we should do yet) we don't need them both in there. He obviously has ability going forward and I really think he can score 5 or 6 goals if he pushes on enough plus influence play going forward. Longer term he has shown for Ireland he also has the ability to be a very good defensive midfield player.
The obvious question of what does he do? I think the season in games he's played well he has been able to neutralise the opposing teams influential players. When Yaya Toure was flying for City McCarthy man marked him and kept him quite quiet. He did similar against Ramsay V Arsenal a couple of seasons ago. When he's at his best he has the energy and drive to make it difficult for opposing players higher up the pitch.
I think increasingly he has shown he too can break from Midfield and influence the game going forward. We need to see more of it. In some games Ross will want/need to come deeper to get the ball, and we need a midfield player willing to break beyond Lukaku or get up to support him. This season hopefully McCarthy can be that man.
As a final point we are a side that is light on leaders. He is a real leader though which can't be underestimated.